Complete Dosage Compensation in Anopheles stephensi and the Evolution of Sex-Biased Genes in Mosquitoes.

Jiang X, Biedler JK, Qi Y, Hall AB, Tu Z - Genome Biol Evol (2015)

Bottom Line:
Furthermore, Culicinae mosquitoes, including the Aedes genus, have homomorphic sex-determining chromosomes, negating the need for dosage compensation.Autosomal and X-linked genes in An. stephensi showed very similar levels of expression in both males and females, indicating complete dosage compensation.In addition, we comparatively analyzed the differentially expressed genes between adult males and adult females in both species, investigated sex-biased gene chromosomal distribution patterns in An. stephensi and provided three examples where gene duplications may have enabled the acquisition of sex-specific expression during mosquito evolution.

evv115-F2: The distribution of the log2 normalized ratio of RPKM values in An. stephensi to their one-to-one orthologs in Ae. aegypti on different chromosome arms in males and females. The width of the violin plots shows the density of genes at different log2 RPKM ratios. Boxplots are also shown in which the bottom and top of the box are the first and third quartiles, and the solid band inside the box is the median. The solid black horizontal line in each panel represents 0 in the corresponding sample. The Dashed black horizontal lines above and below the black line represent +1 and −1.

Mentions:
We calculated the RPKM ratio for each pair of orthologs in An. stephensi and Ae. aegypti. We normalized the median RPKM ratio of An. stephensi autosomal genes to their orthologs in Ae. aegypti to 1 to adjust for differences in the overall expression levels between the species. After normalization, we observed that the median RPKM ratio of An. stephensi X-linked genes to their orthologs in Ae. aegypti was close to 1 in both sexes (fig. 2). These results indicate that there is dosage compensation for the X chromosome in male An. stephensi. The female X-linked gene expression level remained the same indicating that the dosage compensation mechanism is either exclusive to males or has been repressed in females.Fig. 2.—

evv115-F2: The distribution of the log2 normalized ratio of RPKM values in An. stephensi to their one-to-one orthologs in Ae. aegypti on different chromosome arms in males and females. The width of the violin plots shows the density of genes at different log2 RPKM ratios. Boxplots are also shown in which the bottom and top of the box are the first and third quartiles, and the solid band inside the box is the median. The solid black horizontal line in each panel represents 0 in the corresponding sample. The Dashed black horizontal lines above and below the black line represent +1 and −1.

Mentions:
We calculated the RPKM ratio for each pair of orthologs in An. stephensi and Ae. aegypti. We normalized the median RPKM ratio of An. stephensi autosomal genes to their orthologs in Ae. aegypti to 1 to adjust for differences in the overall expression levels between the species. After normalization, we observed that the median RPKM ratio of An. stephensi X-linked genes to their orthologs in Ae. aegypti was close to 1 in both sexes (fig. 2). These results indicate that there is dosage compensation for the X chromosome in male An. stephensi. The female X-linked gene expression level remained the same indicating that the dosage compensation mechanism is either exclusive to males or has been repressed in females.Fig. 2.—

Bottom Line:
Furthermore, Culicinae mosquitoes, including the Aedes genus, have homomorphic sex-determining chromosomes, negating the need for dosage compensation.Autosomal and X-linked genes in An. stephensi showed very similar levels of expression in both males and females, indicating complete dosage compensation.In addition, we comparatively analyzed the differentially expressed genes between adult males and adult females in both species, investigated sex-biased gene chromosomal distribution patterns in An. stephensi and provided three examples where gene duplications may have enabled the acquisition of sex-specific expression during mosquito evolution.